1. Field of the Invention
This invention relates to novel photosensitive anthracene compounds which are polymer-reactive, i.e., contain annular substituents capable of reacting with polymers.
2. Description of the Prior Art
Optical information storage materials play an important role in a variety of practical applications. One such application is information processing, for example, in recording and reading-out of information. The requirements for these materials include good sensitivity to radiation, non-destructive reading-out properties and erasability for repeatable usage. Furthermore, the materials should be easily handled for various types of mechanical processing.
Polymers functionalized with photosensitive groups called "chromophores" have been used for information processing. On irradiation with light, the photosensitive chromophores undergo photoreactions, giving rise to large changes in certain optical properties. In almost all cases, these changes are variations in absorption spectra and/or refractive indices. Except for some special cases, such as polydiacetylene and polyvinylcarbazole, the polymers themselves do not undergo any changes in physical properties on irradiation with light.
The simplest way to prepare polymeric materials containing photosensitive groups is to dope photosensitive molecules, called dopants, into polymer matrices, and to use the whole system as a recording material. This technique has the advantage of avoiding complicated organic syntheses involving chemical attachment of photosensitive groups to polymer chains, but is limited by the compatibility and chemical affinity of the dopants and the polymer matrices. A low level of compatibility can cause aggregation or crystallization of the dopants in the matrices. Such aggregations not only limits the concentration of dopant in a matrix, but also changes the kinetics of photoreactions of the dopant and the optical properties of the material.
Anthracenes, on irradiation with U.V. light, in solution as well as in the crystalline state, dimerize and give the photoproduct, the so-called photodimer, which has optical properties quite different from those of the corresponding anthracenes monomers. Under appropriate conditions, the photodimerization reaction is reversible. U.S. Pat. Nos. 3,807,999 and 3,892,642 describe compounds where two anthracenes are linked together by a flexible chain, which favors dimer formation.